The invention relates to a tinnitus masker with one or more signal generators, a controllable amplifier section, one or two electroacoustic transducers for conversion of electrical signals into acoustic signals as well as a voltage source.
Such devices are already known in principle.
More than half of the world's population suffers from tinnitus in one form or the other. It is a phenomenon which occurs in the hearing system whose causes are still unclear. It may consist of anything from a weak tone which occurs only several times a year up to a continuously audible loud noise, hissing, buzzing or even a very loud tone which is never interrupted.
Tinnitus covers a wide range of phenomena which are all related to the hearing function, and particularly to the middle ear, the organ of Corti, the nerve cells and the nerve tracts as well as to the nerve centers which lead from the organ of Corti to the brain.
The actual causes of tinnitus have not yet been properly established, and it is difficult to localize them exactly.
Recent findings have shown that the nerve centers between the organ of Corti and the brain are responsible for such complex signal processing that an individual nerve cell can be located in the uppermost level of the eighth nerve of the brain which is stimulated only if a quite specific sound is identified by the nerve centers. This sound may be, for example, a quite specific phoneme or a tone with a quite specific frequency. Expressed in other words, it seems to be the task of individual or all nerve cells of this uppermost level to inform the brain that a specific sound or tone or complex tone or sound mixture has occurred. Since the human ear possesses a highly developed capability of distinguishing tones, sounds or noises of different frequencies or frequency mixtures, it is quite possible that a very large number of these nerves are intended for recognition of all those tones which belong to the audible frequency range.
This may be one of the reasons why tinnitus is very frequently perceived as a tone.
In other words, the reason why a patient believes that he is hearing a tone with a specific frequency is apparently that the nerve which would normally transmit a really audible tone of this frequency to the brain is sporadically or continuously stimulated for some reason and then remains in this stimulated condition for either a long or short period of time. This might be caused, for example, by an electromechanical fault or by such "faulty stimulation" in this or a previous nerve cell.
Earlier experiments showed that it was possible in some cases to suppress tinnitus for a certain time or even permanently be exposing the patient to various sounds and/or tones of different kinds and with different sound pressures for shorter or longer time periods. In most cases, pure sinusoidal tones were used either with high sound pressures of short duration or as so-called tinnitus maskers.
A tinnitus masker is an instrument worn on the head or on the body and on the head more or less like a hearing aid which generates a kind of acoustic signal, e.g. a sinusoidal tone, narrow-band noise, broad-band noise or white noise, which is transmitted to the patient either via an earphone or via a miniature receiver which is incorporated in a hearing aid housing. This may be a BTE device, for example.
In other cases, a standard hearing aid has been found useful, since the hearing aid boosts the overall background noise level and thus allows the patient to distinguish this from his tinnitus.
This invention relates only to such tinnitus which is perceived as a tone. In these cases, it is normally possible to identify a specific, often narrow frequency range within which the tinnitus frequency is located.
Using the above methods and techniques, even this still involved quite considerable difficulties for the patient.
If, on the other hand, a tone generator repeatedly and slowly moves through this frequency range, then it may be expected that the true tinnitus frequency is actually and repeatedly produced, although the patient does not exactly know when this is the case.
The task of the invention is thus to create a tinnitus masker of the type mentioned at the start, which appears to be particularly suitable, on the basis of tests, for treatment of the kind of tinnitus mentioned above, which makes itself noticeable by supposed hearing of a tone or tone mixture located in the audio frequency range.
The invention is based on two findings:
1. Residual suppression is recognized only if the masking signal exactly matches the tinnitus signal with respect to frequency content quality. The masking signal must be stronger. PA1 2. Normally, it is extremely difficult for a patient to exactly assess and describe tinnitus quality.